The present invention relates to a catalytic composition which comprises an ERS-10 zeolite, a metal of group VIII, a metal of group VI and optionally one or more oxides as carrier. According to a preferred aspect, the catalytic composition also contains a metal of group II B and/or III A. The catalytic system of the present invention is particularly useful in the upgrading of mixtures of hydrocarbons which boil within the naphtha range containing sulfur impurities, i.e. in hydrodesulfuration with the contemporaneous skeleton isomerization of the olefins contained in these hydrocarbons, the whole process being carried out in a single step. This catalytic system can be used, in particular, for the upgrading of mixtures of hydrocarbons which boil within the naphtha range deriving from cracking processes, preferably mixtures of hydrocarbons having a boiling point within the naphtha range deriving from FCC catalytic cracking (Fluid Catalytic Cracking).
Hydrocarbons which boil within the naphtha range deriving from FCC (i.e. gasoline cut) are used as blending component of gasolines. For this purpose, it is necessary for them to have a high octane number together with a low sulfur content, to conform with the law restrictions which are becoming more and more severe, in order to reduce the emission of pollutants. The sulfur present in gasoline mixtures in fact mainly comes ( greater than 90%) from the gasoline cut deriving from FCC.
This cut is also rich in olefins which have a high octane number. Hydrogenation processes used for desulfuration also hydrogenate the olefins present with a consequent considerable reduction in the octane number (RON and MON). The necessity has therefore been felt for finding a catalytic system which decreases the sulfur content in the hydrocarbon mixtures which boil within the naphtha range and, at the same time, minimizes the octane loss (RON and MON), which can be achieved, for example, by the skeleton isomerization of the olefins present.
The use of zeolites with a medium pore dimension as isomerization catalysts and the consequent recovery of octane in the charges already subjected to desulfuration are known (U.S. Pat. Nos. 5,298,150, 5,320,742, 5,326,462, 5,318,690, 5,360,532, 5,500,108, 5,510,016, 5,554,274, 5,99439). In these known processes, in order to obtain hydrodesulfuration with a reduced octane number, it is necessary to operate in two steps, using in the first step catalysts suitable for desulfuration and in the second step catalysts for recovering the octane number.
U.S. Pat. No. 5,378,352 describes a process in a single step for desulfurating hydrocarbon fractions, with boiling points within the range of gasolines, using a catalyst which comprises a metal of group VIII, a metal of group VI, a zeolite selected from ZSM-5, ZSM-11, ZSM-22, ZSM-23, ZSM-35, ZSM-48, ZSM-50, MCM-22 and mordenite, and a metal oxide as ligand, with a process temperature preferably higher than 340xc2x0 C.
Some catalytic materials containing metals of groups VI and VIII, a refractory carrier and a zeolite selected from ZSM-35, ZSM-5, mordenite and fajasite, are described in EP 442159, EP 437877, EP 434123 for the isomerization and disproportioning of olefins; in U.S. Pat. No. 4,343,692 for hydrodewaxing; in U.S. Pat. No. 4,519,900 for hydrodenitrogenation, in EP 072220 for a process in two steps comprising dewaxing and hydrodesulfuration; in U.S. Pat. No. 4,959,140 for a hydrocracking process in two steps.
We have now surprisingly found a new catalytic system with which it is possible to desulfurate, with high conversion values, mixtures of hydrocarbons that boil within the naphtha range containing sulfur and olefins and contemporaneously obtain the skeleton isomerization of the olefins present. This new catalytic system is also active at temperatures and pressures that are lower than those preferably used in the known art for desulfuration.
Skeleton isomerization enables hydrocarbons to be obtained, which boil within the naphtha range and at the same time with very low RON (research octane number) and MON (motor octane number) losses.
The results obtained do not only relate to the desulfuration of hydrocarbon cuts that boil within the xe2x80x9cheavy naphthaxe2x80x9d range (130xc2x0-250xc2x0 C.), i.e. cuts poor in olefins, but also feeds of xe2x80x9cfull range naphthaxe2x80x9d, which boil within the range of 35xc2x0-250xc2x0 C., i.e. in the case of cuts rich in olefins. In fact, the catalytic system of the present invention has a high selectivity for desulfuration with respect to hydrogenation, which represents an additional advantage in terms of octane recovery in the end-gasoline.
A first object of the present invention therefore relates to a catalytic composition which comprises an ERS-10 zeolite, a metal of group VIII, a metal of group VI, and optionally one or more oxides as carrier.
According to a particular aspect of the present invention, the catalytic composition also comprises a metal of group II B and/or III A. This metal is preferably deposited on the surface of the zeolite.
ERS-10 zeolite is a porous crystalline material described in EP 796821, having in its calcined and anhydrous form a molar composition of oxides corresponding to the following formula:
m M2/nO.z X2O3.YO2
wherein m is a number between 0.01 and 10, M is H+ and/or a cation of an alkaline or earth-alkaline metal with a valence n, z is a number between 0 and 0.02, X represents one or more elements selected from aluminum, iron, gallium, boron, vanadium, arsenic, antimonium, chromium and manganese and Y represents one or more elements selected from silicon, germanium, titanium, zirconium, characterized by the following X-ray diffraction spectrum from powders (recorded by means of a vertical goniometer equipped with an electronic impulse count system and using CuKa radiation (1=1.54178 A) containing the main reflections indicated in Table A:
wherein d indicates the interplanar distance, I/I0.100 represents the relative intensity calculated by measuring the height of the peaks and percentually relating it to the height of the most intense peak, the symble vs indicates a very strong intensity (60-100), s a strong intensity (40-60), m a medium intensity (20-40) and w a weak intensity (0-20).
M is preferably selected from sodium, potassium, hydrogen or their mixtures. According to a particularly preferred aspect of the present invention the ERS-10 zeolite is in acid form i.e. in the form in which the M cationic sites of the zeolite are prevalently occupied by hydrogen ions. It is especially preferable for at least 80% of the cationic sites to be occupied by hydrogen ions. ERS-10 zeolite based on silicon oxide and aluminum oxide, i.e. an ERS-10 zeolite in which X is aluminum and Y is silicon, is preferably used.
According to an aspect of the present invention, when the catalytic composition comprises ERS-10 zeolite and metals of group VI and VIII, said zeolite is preferably present in a quantity ranging from 70 to 90%; when the catalytic composition also comprises one or more oxides as carrier, said zeolite is preferably present in a quantity ranging from 5 to 30% by weight with respect to the total weight of the catalyst.
The catalysts used in the present invention preferably contain Cobalt or Nickel as metal of group VIII, whereas the metal of group VI is preferably selected from molybdenum or tungsten. According to a particularly preferred aspect, Co and Mo are used. The weight percentage of the metal of group VIII preferably varies from 1 to 10% with respect to the total weight of the catalyst, even more preferably from 2 to 6%; the weight percentage of the metal of group VI preferably varies from 4 to 20% with respect to the total weight of the catalyst, even more preferably from 7 to 13%. The weight percentages of the metal of group VI and the metal of group VIII refer to the content of metals expressed as metal element of group VI and metal element of group VIII; in the end-catalyst the metals of group VI and VIII are in the form of oxides. According to a particularly preferred aspect, the molar ratio between the metal of Group VIII and the metal of group VI is less than or equal to 2, preferably less than or equal to 1.
The oxide used as carrier is preferably the oxide of an element Z selected from silicon, aluminum, titanium, zirconium and mixtures of these. The carrier of the catalytic composition can consist of one or more oxides and the oxide used is preferably alumina or alumina mixed with an oxide selected from silica and zirconia.
When the catalyst contains a metal of group II B and/or III A, said metal is preferably present in a quantity ranging from 0.1 to 5% by weight of the total weight of the catalyst, expressed as metal element, even more preferably between 0.1 and 3%. Zinc is preferably used.
The catalytic compositions of the present invention can be prepared with traditional methods, for example by impregnation of the ERS-10 zeolite with a solution containing a salt of a metal of group VI and a salt of a metal of group VIII, drying and calcination. The impregnation can also be effected using a solution containing a salt of a metal of group VI and a solution containing a salt of a metal of group VIII.
By means of impregnation of a solution containing a salt of a metal of group II B and/or III A, catalytic compositions can be prepared which contain, in addition to the zeolite, metal of group VI and metal of group VIII, also a metal of group II B and/or III A.
When the catalyst contains one or more oxides as carrier it can be prepared by mixing the zeolite with the oxide, followed by extrusion, calcination, an optional exchange process which reduces the sodium content, drying, impregnation with a solution containing a salt of a metal of group VI, drying, calcination and impregnation with a solution of a salt of a metal of group VIII, drying and calcination.
According to a particularly preferred aspect of the present invention, the catalytic compositions which contain one or more oxides as carrier are prepared by means of the sol-gel technique as follows:
a) an alcoholic dispersion is prepared, containing a soluble salt of the metal of group VIII, ERS-10 zeolite and one or more organic compounds capable of generating the supporting oxide or oxides;
b) an aqueous solution is prepared containing a soluble salt of the metal of group VI and, optionally, tetraalkylammonium hydroxide having the formula R4NOH;
c) the alcoholic dispersion and the aqueous dispersion are mixed and a gel is obtained;
d) aging of the gel at a temperature ranging from 10 to 40xc2x0 C.;
e) drying of the gel;
f) calcination of the gel.
The catalytic compositions thus obtained have a high surface area ( greater than 200 m2/g) and a high pore volume ( greater than 0.5 cm3/g) with a distribution within the mesoporosity range.
In step a) of this preparation, the metal salt of group VIII is, for example, a nitrate, a hydroxide, an acetate, an oxalate, and preferably a nitrate. When a catalytic composition also containing a metal of group II B and/or III A is desired, a salt of this metal will also be present in the alcoholic dispersion.
The organic compound capable of generating the supporting oxide or oxides, by means of hydrolysis and subsequent gelations and calcination, is preferably the corresponding alkoxide or alkoxides, in which the alkoxide substituents have the formula (Rxe2x80x2O)xe2x80x94 wherein Rxe2x80x2 is an alkyl containing from 2 to 6 carbon atoms. The alkoxide is preferably an element Z selected from silicon, aluminum, titanium, zirconium and their mixtures; in particular, when Z is aluminum, it is a trialkoxide having the formula (Rxe2x80x2O)3Al, wherein Rxe2x80x2 is preferably an isopropyl or a sec-butyl; when Z is silicon, it is a tetraalkoxide having the formula (Rxe2x80x2O)4Si wherein Rxe2x80x2 is preferably ethyl and, when Z is Zr, it is an alkoxide having the formula (Rxe2x80x2O)4Zr wherein Rxe2x80x2 is preferably isopropyl.
In step b) the soluble salt of the metal of group VI can be an acetate, an oxalate or ammonium salts, and is preferably an ammonium salt. The tetraalkylammonium hydroxide has the formula R4NOH wherein R is an alkyl group containing from 2 to 7 carbon atoms. According to a preferred aspect the solution in step b) also contains formamide (Drying Control Chemical Agent) which favours the stabilization of the porous structure during the drying phase.
The quantities of the reagents are selected in relation to the composition of the end-catalyst.
In step c), according to the preferred sequence, the solution of step b) is added to the suspension of step a).
In step d) the gel obtained is maintained at a temperature ranging from 10 to 40xc2x0 C., for a time of 15-25 hours.
Step e) is carried out at a temperature ranging from 80 to 120xc2x0 C.
Step f) is carried out at a temperature ranging from 400 to 600xc2x0 C.
According to another aspect of the present invention, the catalytic system containing one or more oxides as carrier can be prepared as follows:
a) an alcoholic dispersion is prepared, containing ERS-10 zeolite and one or more organic compounds capable of generating the supporting oxide or oxides;
b) an aqueous solution is prepared containing tetraalkylammonium hydroxide having the formula R4NOH;
c) the alcoholic dispersion and the aqueous dispersion are mixed and a gel is obtained;
d) aging of the gel at a temperature ranging from 10 to 40xc2x0 C.;
e) drying of the gel;
f) calcination of the gel;
g) impregnation of the calcined product with a solution containing a salt of a metal of group VI, drying, calcination and impregnation with a solution of a salt of a metal of group VIII, drying and calcination.
The quantities of the reagents are selected in relation to the composition of the end-catalyst. The reagents used are the same as the sol-gel synthesis.
According to another aspect of the present invention, the catalytic compositions containing the supporting oxide or oxides can be prepared as follows:
a) an alcoholic dispersion is prepared, containing a soluble salt of the metal of group VIII and one or more organic compounds capable of generating the supporting oxide or oxides;
b) an aqueous solution is prepared containing a soluble salt of the metal of group VI and, optionally, tetraalkylammonium hydroxide having the formula R4NOH;
c) the alcoholic dispersion and the aqueous dispersion are mixed and a gel is obtained;
d) aging of the gel at a temperature ranging from 10 to 40xc2x0 C.;
e) drying of the gel;
f) mechanical mixing of the dried product with ERS-10zeolite;
g) calcination.
The reagents used are the same as the sol-gel synthesis.
The quantities of the reagents are selected in relation to the composition of the end-catalyst.
The latter preparation is that preferably used for the synthesis of the catalytic composition of the present invention which also contains a metal of group II B and/or III A deposited on the surface of the zeolite.
In this case, in step f) an ERS-10 zeolite is used, on whose surface a metal of group II B and/or III A has been deposited by impregnation, using the known techniques. The ERS-10 zeolite thus modified is new and is a particular aspect of the present invention.
According to another aspect of the present invention, the catalytic compositions containing one or more oxides as carrier can be prepared as follows:
a) impregnation of the carrier, consisting of one or more oxides, with a salt of a metal of group VI and with a salt of a metal of group VIII,
b) drying and calcination of the material obtained in step a),
c) mixing of the impregnated oxide obtained in step b) with the ERS-10 zeolite.
The quantities of the reagents are selected in relation to the composition of the end-catalyst.
The impregnations of step a) are carried out with any traditional method, the salts of metals of groups VI and VIII are in aqueous solution. When separate aqueous solutions for the metal of group VI and for the metal of group VIII, are used, a drying and calcination step can be inserted between the two impregnations. Before step c) the impregnated oxide can be ground and sieved into particles of  less than 0.2 mm and then, in step c), mixed with the zeolite by physical mixing or dispersing the particles in an organic solvent of the cyclohexane or cyclohexanol type. The solvent is vaporized and the particles of catalyst dried and calcined. The mixing of step c) can also be carried out by mixing and homogenizing a solid mixture comprising the impregnated oxide (with particle dimensions of  less than 0.2 mm), the zeolite, a ligand and, optionally, combustible organic polymers.
The mixture thus obtained can be mixed with a peptizing acid solution, extruded and calcined with any traditional method. Alternatively, the paste can be pelletized, dried and calcined with any traditional method.
The catalysts used in the process of the present invention can be used as such or, preferably, extruded according to the known techniques, for example using a peptizing agent, such as a solution of acetic acid, and optionally a ligand of the pseudobohemite type, added to the catalyst to form a paste which can be extruded. In particular, when the catalysts are prepared by sol-gel, the addition of the ligand is not necessary during the extrusion process.
The materials of the present invention can be used as catalysts for the upgrading of hydrocarbon mixtures which boil within the naphtha range, and even more generally within the range C4 and 250xc2x0 C.
A further object of the present invention therefore relates to a hydrodesulfuration process of hydrocarbon mixtures having boiling ranges within the range of C4 to 250xc2x0 C., containing olefins and at least 150 ppm of sulfur, with the contemporaneous skeleton isomerization of these olefins, effected with hydrogen in the presence of a catalytic composition which comprises an ERS-10 zeolite, a metal of group VIII, a metal of group VI, and optionally one or more oxides as carrier. According to a particular aspect of the present invention the catalytic composition also comprises a metal of group II B and/or III A, preferably deposited on the surface of the zeolite.
When the catalytic composition containing the ERS-10 zeolite, a metal of group VI, a metal of group VIII, and optionally a metal of group II B and/or III A, is used, the process of the present invention is carried out at a temperature ranging from 220 to 360xc2x0 C., preferably between 300 and 350xc2x0 C., at a pressure ranging from 5 to 20 kg/cm2, at a WHSV ranging from 1 to 10 hoursxe2x88x921. The quantity of hydrogen is between 100 and 500 times the quantity of hydrocarbons present (Nl/l).
When the catalytic composition also contains one or more oxides as carrier, the hydrodesulfuration process and contemporaneous skeleton isomerization of the olefins present is carried out at a temperature ranging from 220 to 320xc2x0 C., preferably between 250 and 290xc2x0 C., at a pressure ranging from 5 to 20 kg/cm2, and a WHSV between 1 and 10 hoursxe2x88x921. The quantity of hydrogen is between 100 and 500 times the quantity of hydrocarbons present (Nl/l).
The hydrocarbon mixture which can be desulfurated according to the present invention contains more than 150 ppm of sulfur. For example hydrocarbon mixtures with a sulfur content of more than 600 ppm, or even higher than 10,000 ppm can be subjected to hydrodesulfuration.
The hydrocarbon mixtures which are subjected to hydrodesulfuration according to the process of the present invention are mixtures having boiling ranges within the range of C4 to 250xc2x0 C., C4 referring to the boiling temperature of a mixture of hydrocarbons with four carbon atoms. Mixtures of hydrocarbons which boil within the naphtha range, i.e. having boiling ranges within the range of C5 to 220xc2x0 C., are preferably subjected to hydrodesulfuration.
The catalysts of the present invention are activated, before use, by sulfidation according to the known methods. According to a particular aspect of the present invention, it is possible to effect the desulfuration and isomerization process in a reactor in which the catalytic composition is divided in two beds, the first containing the ERS-10 zeolite, which may optionally contain a metal of group II B and/or III A, the second containing the remaining catalytic component containing a metal of group VI, a metal of group VIII and one or more oxides as carrier.
The following examples describe different preparations of catalysts of the present invention and upgrading tests on both the model charge and on full range naphtha from FCC. An ERS-10 zeolite in acid form, prepared as described in example 1 of EP 796821, having a molar ratio SiO2/Al2O3=67, is used in all the examples.